This invention relates to fluid sampling devices and more particularly to blood collection containers for drawing blood samples.
Evacuated containers or tubes having needle pierceable stoppers are used extensively in drawing blood samples for the purpose of conducting laboratory tests on the patient's blood. A conventional method of obtaining a sample is to employ a blood collection tube and a tube and needle holder having a double-ended needle cannula. After the distal end of the cannula is placed in the vein of the patient, the air evacuated blood collection tube is moved in the holder with the tube stopper being guided onto the proximal end of the cannula. The cannula pierces the stopper and the negative pressure in the container facilitates the drawing of blood from the vein of the patient.
In many cases, a number of evacuated containers are filled with blood samples while using the same tube holder and while the cannula remains in the vein of the patient. For example, containers provided with different chemicals may be used to draw a number of blood samples for the purpose of conducting different clinical tests on the patient's blood. Care must be taken to avoid the flowback of drawn blood to the patient since these chemicals may be harmful to the patient. Also, non-sterile tubes are usually used.
When employing conventional tube and needle holders and evacuated collection tubes, faulty techniques in drawing blood can cause withdrawn blood to be returned to the patient. For example, if the contents of the tube is allowed to contact the proximal end of the needle and an employed tourniquet is not removed soon after blood begins to flow or if the arm of the patient is raised, a drop in venous pressure may cause the flowback of blood from the tube to the patient. Also, if a force is applied to the tube in a manner to compress the stopper against the holder while the tube contains blood, a pumping effect may be produced causing withdrawn blood to flow back into the patient.
Valves have been provided in the needle assembly of sampling devices to prevent the backflow of drawn blood from the container or tube to the patient. U.S. Pat. No. 3,874,367, for example, shows a valve disposed in a chamber constructed in a needle assembly between distal and proximal needles for preventing withdrawn blood from returning to the patient. This construction, however, is relatively expensive not only because of the new tooling required in the manufacture of such needle assemblies but because of the additional parts required. Such devices require two needles, two hubs, and the steps of securing each needle to its hub. Such parts and steps result in relatively high manufacturing costs.